Attempts have been made to reduce or mask noise generated during a brake application through the application of a sound coating on backing plates as disclosed in U.S. Pat. No. 3,998,301, the location of a screen member between the friction member and backing plate as disclosed in U.S. Pat. No. 4,154,322, the use of discrete friction members as disclosed in U.S. Pat. No. 4,315,563, selecting the shape of a friction pad whose engagement surface is less than the nodal diameter of a frequency that would create undesirable noise as disclosed in U.S. Pat. No. 4,705,146 and through modification of ingredients in the friction material. The methods and structure to reduce noise as disclosed in the prior art has not been widely accepted by the automobile industry primarily because of the added cost associate for such brake systems.
It is known that most structures vibrate and such vibration is often the result of dynamic forces applied to such structures. The vibration of the structures in frequency domain is a product of the structure response spectrum and the spectrum of the applied dynamic force. This is the basis of frequency response analysis. The structure response can be studied by modal analysis through which the modal parameters of the structure (natural frequencies, modal damping and mode shapes) can be identified, and ultimately a modal model of the structure can be constructed based on these modal parameters. From experimentation it has been determined that noise can essentially be generated with each brake system under specific force applications of the associated friction pads.